Magnetic field-line reconnexion by localized enhancement

It is demonstrated by numerical experiment that the evolutionary process of magnetic field-line reconnexion by a localized enhancement of resistivity is eventually checked, with the system attaining a quasi-steady state. On the basis of the quasi-steady configuration, established from an initially antiparallel magnetic field, the MHD properties that are characteristic of the diffusion, field reversal and external regions, respectively, and then the mutual dependence among them may be clarified. The physical processes in the diffusion region are especially note-worthy, since the ultimate cause for the present reconnexion process is the bending of the field lines towards the magnetic neutral point, which results from the locally enhanced resistivity assumed in the diffusion region. The present numerical results generally agree with the analytical results for the steady reconnexion, although some discrepancies exist owing to the differences of the postulated basic situations between them. It is pointed out that changes in flow properties across the boundary of the field reversal region agree well with those required for a slow mode compression wave and that the dominant process in the external region corresponds to a fast mode expansion. (author)